1. Field of the Invention
The present invention relates generally to the field of aerodynamics, and more particularly to methods and systems for improving aerodynamic performance through active boundary layer control.
2. Description of Related Art
Considerable research has been conducted in the field of aerodynamics toward reducing drag and delaying stall. Delaying stall allows an airplane to fly more slowly at a given angle of attack or to fly at a higher angle of attack for a given speed. A lower stall speed increases the factor of safety for any takeoff or landing, and also allows for shorter takeoffs and landings. Shorter takeoff and landing requirements may allow smaller airports to accommodate larger aircraft, thereby decreasing the traffic around large international airports and increasing passenger convenience and safety. Modern aircraft commonly utilize complex flap arrangements to delay stall. These flap arrangements, however, typically are heavy and expensive to produce and maintain. Accordingly, it would be advantageous to eliminate the need for flap arrangements or decrease their size and complexity.
Reduction of drag reduces the thrust requirements on an aircraft""s engines, and increases fuel economy. In addition, decreased drag increases the maximum cruising speed of an aircraft. Trip times may thereby be reduced without increasing fuel consumption. As a result, a smaller, faster fleet can handle the same amount of traffic as a larger, slower fleet. Additionally, a more efficient airplane reduces operation and maintenance costs, further improving a carrier""s profitability.
Active boundary layer control is a relatively new area of research in the field of aerodynamics. The relative velocity of the fluid flowing over an aerodynamic surface increases across the boundary layer, from zero at the surface to the maximum velocity at the edge of the boundary layer. Drag is decreased by minimizing the boundary layer and reducing separation of the boundary layer from the surface.
Piezoelectrics have recently emerged as a promising alternative to conventional methods of aerospace device actuation. Piezoelectrics have proven their versatility in many aspects of aerospace engineering, including control and the minimization of weight. In addition, piezoelectric panels have been used to increase or decrease drag by moving the panel towards or away from the ambient fluid. Piezoelectric synthetic jet actuators (Pjets), also called massless jets, typically include a plenum or cavity with a jet orifice and a diaphragm that is vibrationally driven by a piezoelectric actuator. As the diaphragm vibrates, ambient fluid is typically drawn into the plenum through the jet orifice on each downstroke of the diaphragm, and is discharged from the plenum through the jet orifice on each upstroke of the diaphragm. Experiments have been conducted wherein Pjets are embedded within an object to direct airflow normal to the flow of ambient fluid along the surface of the object. These Pjets ingest and expel air through the same slots, causing a recirculation region to form around the actuator that in turn changes the aerodynamic shape of the object. To date, however, these experiments have not focused on the reduction of drag and postponement of stall on an airfoil, and the direction of discharge tangentially to the flow over an airfoil. Accordingly, significant advantage remains to be discovered and optimized in the field of active boundary layer control.
Thus, it has been found that needs exist for improved systems and methods for reduction of drag and postponement of stall on an aerodynamic object through active boundary layer control. It is to these and other needs that the present invention is primarily directed.
Briefly described, in its preferred embodiments, the present invention relates generally to systems and methods for improved reattachment of the boundary layer to an airfoil surface as the angle of attack is increased, delaying stall, and reducing drag. One aspect of the invention provides a trailing edge-mounted apparatus to prevent air from creeping around the trailing edge from the underside of a wing. Another aspect of the invention uses piezoelectric synthetic jet actuators (PJets) to ingest air into the wing and then expel that air tangentially to the surface of the wing. This prevents any major disturbances in the boundary layer reattachment and flow downstream of the Pjets, and in a sense the arrangement acts as a boundary layer pump, blowing the boundary layer downstream before it can detach. In this manner, drag may be reduced and the wing may reach higher angles of attack before stall.
In one embodiment, the present invention is an aerodynamic object including at least one surface having a leading edge and a trailing edge, and defining a length between the leading edge and the trailing edge. The object also includes at least one chamber within the object, and at least one piezoelectric synthetic jet actuator for drawing fluid into the chamber through an intake and discharging fluid from the chamber through an outlet.
In another embodiment, the present invention is an aerodynamic object including a boundary layer pump for ingesting air at a first location and expelling air at a second location remote from the first location.
Another embodiment of the present invention is a method of improving performance of an aerodynamic object, the method including ingesting air at a first location on the object and expelling air at a second location remote from the first location.
In another embodiment, the present invention is an airfoil including a leading edge and a trailing edge, and defining a length between the leading edge and the trailing edge. The airfoil preferably also includes at least one internal chamber and at least one piezoelectric synthetic jet actuator for drawing fluid into the internal chamber through a first intake and discharging fluid from the internal chamber through a first outlet. The first outlet is preferably located between the first inlet and the leading edge, and the fluid is discharged from the first outlet in a direction generally parallel to an adjacent external surface of the airfoil.
These and other features and advantages of preferred forms of the present invention are described herein with reference to the drawing figures.